Significant challenges, notably material handling issues, are encountered when solidifying ex situ or in situ deposits, especially but not necessarily subterranean deposits, of wet oily organic waste that contains compounds that can interfere with solidification, such as vegetable and mineral oils, various oily hydrocarbons and oily derivatives thereof when present at concentrations above about 100 ppm. For example, after excavating oil-contaminated solids from an waste source (or ‘hot spot’), an aqueous oily slop that remains is solidified to minimize contaminant mobility, as a requirement for site closure, and to shore up the ground above the excavation.
U.S. Pat. No. 4,726,713, incorporated herein by reference in its entirety as if set forth herein, discloses methods for solidifying waste to produce a low permeability solid mass with high load-bearing unconfined compressive strength (UCS) using a self-hardening slurry formed from a dry mix that contains, for example, attapulgite clay and ground blast furnace slag cement. A dry mix containing attapulgite and blast furnace slag cement for, inter alia, stabilizing or solidifying wet soil, solid wastes, and sediment is marketed commercially by Liquid Earth Support, Inc. under the brand name Impermix®.
The methods of the '713 patent for solidifying ordinary wet solid wastes are most effective at approximately 95-100° F. (ambient temperature in the summer months at some latitudes), but are less effective at ambient temperatures at or below about 65° F., and are still less effective at temperatures approaching freezing when the wet waste is contaminated with oily materials. For treating oil-contaminated waste, the '713 solidification process is only effective with curing at approximately 100° F.
The vendor of Impermix® recommends heating the waste matrix by adding hot water or steam, but this is operationally ineffective and cost prohibitive for large treatment areas, particularly for in situ subsurface treatment areas, and even more particularly in low temperature environments. Further, treatment at such high temperatures can cause toxic organic compounds in oily waste to become volatile and to be released from the waste.
It has also been suggested to solidify wastes that contain oily organic matter by adsorbing the organic matter to powdered activated carbon (PAC) in the '713 process, so that it takes on the solid properties of the carbon. Such treatment requires high PAC dosages and, again, is cost prohibitive for in large, in situ subsurface treatments.
Still further, highly alkaline materials such as caustic soda (NaOH) or lime (CaO) can be added to oil-contaminated waste to increase pH and accelerate solidification, but such materials cannot be added when the waste contains amphoteric heavy metals, such as lead, which are more mobile under alkaline conditions.
Methods are also known for using Portland cement (PC) to solidify an oily waste (for example, see U.S. Pat. Nos. 3,947,284; 3,980,558 and 4,209,335, each incorporated by reference herein as if set forth in its entirety). U.S. Pat. No. 5,584,792, also incorporated herein by reference as if set forth in its entirety, discloses using a combination of fly ash and circulating fluid bed combustion ash in a process for stabilizing oily petroleum refining wastes. U.S. Pat. No. 4,514,307 discloses using lime and fly ash in a process for solidifying and stabilizing waste that comprises non-biological organic compounds.
Still needed in the art are processes for solidifying wet oil-contaminated wastes in situ and ex situ, especially processes for solidifying waste that contains one or more amphoteric heavy metal, without promoting contaminant mobility or release of volatile organic compounds.